1. Field of the Invention
The present invention relates to an information processing apparatus for generating a scanning instruction for visible information which is formed on a recording medium by scanning a laser.
2. Description of the Related Art
A technology of writing characters and symbols onto a medium such as a paper sheet with a laser is put in practical use. As it has become possible to render characters on a medium such as a sheet, it has become easy to render characters onto labels of containers at factories. Furthermore, rewritable type heat-sensitive paper (hereinafter, “rewritable paper”) on which rendering and erasing can be repeatedly performed, is put in practical use. For example, considering a container used in physical distribution, the destination of the same container may not always be the same, and therefore if characters on a label are erased and new characters are rendered while the label remains pasted on the container, the need of replacing labels can be significantly reduced.
However, rewritable paper is characterized in that a color is erased by heat of a certain temperature, and a color appears when heat of a higher temperature is applied. However, when excessive thermal load is applied, the rewritable paper becomes altered, and deterioration may occur, such as the shelf life may be reduced or the erasing may not be completely performed. Excessive thermal load is applied when heat is additionally applied to a part that already has high temperature. On a label, excessive thermal load is apt to be applied at parts where characters and symbols intersect or where adjacent parallel lines are formed for filling in an area.
FIG. 24 illustrates an example of a character rendered on rewritable paper. In FIG. 24, a Japanese katakana character “nu” is rendered. The Japanese character “nu” includes a turning edge point 320 and an intersection point 310. At the intersection point 310, the laser is radiated again at the same position while there is remaining heat of the stroke rendered immediately before the present stroke, and therefore the temperature of the intersection point 310 is further increased. Furthermore, at the turning edge point 320, due to the impact of the inertia of the mirror for controlling the direction of radiating a laser, the laser is radiated for a relatively long time, and therefore the temperature at the turning edge point 320 increases.
Accordingly, when a laser radiating device radiates a laser beam on rewritable paper, there are cases where control is implemented to prevent an excessive thermal load from being applied (see, for example, Patent Documents 1 through 3). Patent document 1 discloses a recording method of scanning a laser beam so that a subsequent line is rendered after passing the line previously rendered, at portions where lines overlap each other. Patent Document 2 discloses a record erasing device for reducing at least one of the power and the radiating time of the laser beam radiated onto an intersecting render point when there are two lines that intersect each other. Patent Document 3 discloses a recording method by intersection point removal, which involves not radiating a laser beam for one of overlapping render lines at a portion where render lines of a character overlap.
On rewritable paper, at portions other than portions where a laser beam has been radiated, a color may also be formed due to residual heat.
FIG. 25 illustrates the impact of residual heat when the intervals between lines are narrow. Arrows in FIG. 25 indicate the scanning positions and scanning directions of laser beams. The light spots (radiation parts) of laser beams are extremely small, but at portions other than the radiated portions, a color may also be formed due to residual heat. As shown in FIG. 25, the space between line 1 and line 2 is narrower than the space between line 2 and line 3. When a space is as narrow as the space between line 1 and line 2, the lines contact each other due to residual heat, which reduces the legibility of the render object. Furthermore, the temperature may increase at the portions where color is formed due to the residual heat of the two lines.    Patent Document 1: Japanese Laid-Open Patent Publication No. 2006-306063    Patent Document 2: Japanese Patent No. 3990891    Patent Document 3: Japanese Laid-Open Patent Publication No. 2008-179135